Inertial guidance systems require accelerometers capable of accurately measuring the magnitude and direction of acceleration. Typically, the accelerometers must have a dynamic range of 10.sup.5 gravities or more, be rugged enough to withstand the hostile environment, and be small and lightweight.
In attempts to meet the needs for accuracy and dynamic range, accelerometers having quartz resonator elements have been developed. See, for example, U.S. Pat. Nos. 3,479,536 and 3,238,789, incorporated herein by reference. In those devices, the quartz resonator is rigidly attached to a separate supporting structure at one end and a separate proof mass at the other. Typically, only the resonator is quartz.
Although the accelerometers with quartz resonators-may have the desired dynamic range and stability, they are typically extremely difficult to manufacture and very costly. These problems are primarily directly attributable to the manner in which the quartz resonator is configured. The resonator must be physically coupled to the other elements of the accelerometer, which may be constructed of materials having a different coefficient of thermal expansion than the quartz resonator material. Without intricately machined components, as the accelerometer undergoes temperature changes, the resonator may experience additional loading not attributable to acceleration, leading to erroneous readings. That loading would exist even if the accelerometer included separate temperature sensors for compensating the acceleration reading.
In order to meet the accuracy requirements, the separate accelerometer components must be fabricated with high dimensional precision and assembled with the same degree of precision, all at great expense. The number and type of components also increases the size and weight of the accelerometer, which is undesirable in a missile guidance system. The very fact that a large number of separate parts is employed also affects the ruggedness of the accelerometer.